PLANT-SPECIFIC CALMODULIN-BINDING PROTEINS

Calmodulin CaM is a ubiquitous Ca 2+ sensor protein (16 to 18 kD) with no catalytic activity that can, upon binding Ca 2+ , activate target proteins involved in various cellular processes. The CaM prototype is comprised of two globular domains connected with a long flexible helix. Each globular domain contains a pair of intimately linked EF hands. One EF hand motif is composed of a specialized helix-loop-helix structure that binds one molecule of Ca 2+ . ( CaM calmodulin ) is the most prominent Ca 2+ transducer in eukaryotic cells, regulating the activity of numerous proteins with diverse cellular functions. Many features of CaM and its downstream targets are similar in plants and other eukaryotes. However, plants possess a unique set of CaM-related proteins, and several unique CaM target proteins. This review discusses recent progress in identifying plant-specific CaM-binding proteins and their roles in response to biotic and abiotic stresses and development. The review also addresses aspects emerging from recent structural studies of CaM interactions with target proteins relevant to plants.